I presume you mean the colour clothing like an M-1941or M-1943 Parson's jacket would be, (e.g the jacket Tom Sizemore and most of the other soldiers wear in the movie Saving Private Ryan).

With Humbrol paints, I'd try something like using a combination of Humbrol's matt colours No 72 (which is khaki drill) -maybe lighten that up a bit with flat white and use it as a base coat, and then drybrush highlights with Humbrol No 121 (which is pale stone). I reckon that would get you pretty close for a start before doing some more sophisticated weathering, I'd be tempted to dust things up with pastels too. If you like very pale 'scale colours', you could try the Humbrol No 121 as a base coat, then drybrush with some of it lightened up a lot.

From a realism standpoint, you should bear in mind that, unlike in movies where you see those jackets looking quite cool, the real clothes were pretty disgusting and grimy a lot of the time for many troops (particularly during the Normandy landings) when they were quite often treated with CC-2 anti-gas paste in an attempt to protect against some of the more nasty gasses the Germans developed, such as Sarin (but did not actually use in combat). The paste made them horrible and greasy. The first waves of troops onto the beaches at Normandy would have likely had that CC-2 paste on their clothes.

To spot what clothing looks like when treated in that way on period pictures, if you see a soldier (typically an NCO) with a brown paper disposable brassard on his shoulder, then it is likely he'll also have clothing treated with anti-gas paste, because the paper brassard was a gas detection device which changed colour when gas was present (they usually carried a spare disposable brassard in their gas mask bag along with the mask itself). It was a sort of dark manilla brown colour, similar to the diamond shaped patch that could be seen applied to the wings of Spitfires and Hurricanes in 1940, when, as with Normandy, the Allies expected the Germans to use gas attacks.